1. Field of the Invention
This invention relates to filling tools (so-called caulking guns) used mainly for repairing operations of building materials or the like for the purpose of waterproofing, such as repairing operations of cracks or gaps in the outer wall of a residential building and repairing operations of a joint between a bathtub and a wall surface of a bathroom, by filling materials, such as a silicon type filling material, (hereinafter simply referred to as caulking materials).
2. Description of the Related Art
For example, a caulking material known as a silicon sealant is commercially available on the market in a form of a cartridge filled with a fixed amount of the material. The cartridge may be set in a dedicated caulking gun to be used for the filling operation.
In general, the caulking gun includes a lever in the form of a trigger that can be pulled by the user grasping a handle portion of the caulking gun to move an push rod, whereby the caulking material can be extruded from a nozzle of the cartridge. In the case of this completely manual type caulking gun, great fatigue is involved as a result of the repetition of the extruding operation. In view of this there has been provided an electric caulking gun using an electric motor as a drive source. Techniques related to this electric caulking gun are disclosed, for example, in JP-A-8-257465 (also published as Japanese Patent No. 3598565), JP-A-58-137465, and U.S. Pat. No. 4,615,469 (Also published as JP-A-59-222251). In the electric caulking guns as disclosed in these publications, the electric motor is started to move the push rod when a switch lever is operated to be turned on. Therefore, unlike the manual type caulking gun, in which the operation force of the lever generates the extrusion force, the user can easily perform the filling operation repeatedly.
However, the electric caulking guns potentially involve a problem of so-called after-dripping, in which some caulking material is discharged due to the residual pressure inside the cartridge immediately after the stopping of the electric motor. JP-A-8-257465 discloses a technique for inhibiting the problem of after-dripping. According to an after-dripping prevention mechanism disclosed in this publication, the electric motor is reversed immediately after the of operation, so that the push rod is forcibly restored to thereby release the residual pressure inside the cartridge, whereby it is possible to prevent after-dripping.
However, because the electric motor is reversed to forcibly restore the push rod in the case of this after-dripping prevention mechanism, a gap may be generated between the rear end surface of the cartridge (the surface to be pressed by the push rod) and the front end of the push rod. Thus, when the electric motor is started again, the push rod moves idle by an amount corresponding to this gap before being pressed against the rear end surface of the cartridge, with the result that there is generated a time lag (a delay) by an amount corresponding to this idle movement (i.e., corresponding to the gap).
Therefore, there has been a need in the art for a technique of inhibiting the after-dripping without causing a time lag in pressing a cartridge by a push rod.